London: Owning a puppy, having a happy marriage and plenty of good friends hold the secret to longevity, according to a landmark study. All these are more important than where you were born, whether you were born into a wealthy or poor family or what social class you are in, the Grant study found.

The Grant Study is a 68-year study which followed more than 200 young, white, healthy American men from youth to old age, with evaluations taking place every two years, the reported.

The report found that longevity has far more to do with happiness than social class. The current director of the study, George Vaillant from Harvard Medical School, told BBC Radio Four's Today programme that fulfilling relationships were the key to a happy and long life, adding that only four of the 31 single men in the study were still alive today, compared with more than a third of those in 'good relationships'.

"Having a loving family is terribly important, but from 70 to 90 years old you'd be surprised at the people who, despite enormous deprivation, manage to find love later on," he added. "If you want to be happy, and don't have a six-month-old baby to trade smiles with, get yourself a puppy," he said.

"The finding on happiness is that happiness is the wrong word. The right words for happiness are emotional intelligence, relationships, joy, connections and resilience," he said.

The report also found that marriages bring much more contentment after age 70, and how we age after 80 is more about habits formed before the age of 50, rather than genetics.

"The credit for growing old with grace and vitality, it seems, goes more to us than to our stellar genetic makeup," Vaillant said. Previous research has found that owning a pet dog improves your physical and mental wellbeing more than having a cat.

Researchers from Queens University, Belfast, concluded that dogs can prevent us from getting ill (by boosting the immune system) and help us recover more quickly when we do fall ill. There are also the obvious benefits of getting regular exercise.